The present invention relates to the rapid rate reactive sputtering of titanium and like metallic nitrides onto a substrate or workpiece. The field of this invention comprises substrate coating by cathodic magnetron sputtering and includes a substrate to be coated, a coating material mounted on a target plate, electrode plates causing gas plasma particles to strike the target to release the coating material, means to control the rate of deposition of the coating material, and means to carry the article to be coated and to expose the desired portions for coating. The prior methods for coating substrates with thin metallic films have been accomplished by vapor deposition, plasma spray processes and cathode sputtering.
Vapor deposition processes to provide a metallic thin film on a workpiece utilize the material to be plated which is heated in a suitable atmosphere, such as in a vacuum or an inert shielding gas, to such an extent that the material evaporates and is deposited as a film on a substrate. Plasma spray processes provide the material to be deposited as a fine-grained powder which is brought into a plasma arc so that the particles melt and are deposited on a substrate.
Cathode sputtering or radio-frequency ionic sputtering involves a target of the material to form the coating in a gas discharge wherein the material is sputtered by ion bombardment; the particles removed from the target being deposited on the substrate. The target becomes the cathode and an anode is located beyond the substrate. Thus particles moving from the cathode toward the anode strike the substrate. Where a thin film of metallic compounds, such as the oxides, nitrides, carbides and the like, are to be deposited on various substrates, reactive sputtering is used wherein the target consists of the metal for the plating compound. A neutral gas, such as argon, is mixed with a reactive gas such as oxygen, nitrogen or methane. The particles that are dislodged from the target combine with the reactive gas to produce the desired compound which is plated on the substrate or workpiece.
A major problem in the sputtering process is an abrupt decrease in the deposition rate of metallic films during the sputtering process in a reactive gas atmosphere. The deposition rate using a reactive gas was found to be 10 to 20% of the rate for the deposition of pure metal in a neutral gas. One method developed to increase the deposition rate for reactive sputtering of titanium nitride is by the "pulsing" of the nitrogen gas, that is, admitting the gas in successive, controlled volumes. In this method the gas is admitted to the chamber for a pulse duration of 2 to 3 seconds and then shut off for 2 to 3 seconds. Using this pulsing technique, the nitride film deposition rate was increased substantially to approximately 50% to 70% of the deposition rate of the pure metal. The present invention expands on this pulsing technique to provide a continuous flow of the reactive gas, as contrasted to a pulsed or intermittent flow, and further enhance the nitride deposition rate to achieve substantially 100% of a deposition rate of the pure metal.